The aim of this project is to clarify processes of attention and memory as these affect visual search and discrimination. Attention is central to information processing in humans and other animals; deficits or disruptions of attention are thought to play a role in a number of cognitive disorders in humans. The research adops a widely-held theorectical view that attention involves the retrieval of memories (representations or "search images") of important stimuli in the environment; the experiments use a tractable, informative animal model in which to explore this matter. Pigeon subjects are supplied with advance information about upcoming search or detection targets. This information is given in the form of stimulus cues or situational context. By manipulating cues and contexts, the experiments explore the nature of the hypothesized stimulus representations and the memory retrieval processes through which they are activated. An exemplar model of discrimination and attention attempts to predict key results of these experiments and integrate them with other discrimination data.